Foreign key constraints with MySQL/InnoDB

I am try to do some performance testing with varchar foreign keys vs int foreign keys and was wondering how foreign key constraints effect performance of MySQL.

I assume that they effect inserted/updates to a degree however I am not to worried about that in my testing. I was wondering if they effect SELECT statements and if they effect data/index size?

"integers are cheaper to compare than characters, because character sets and collations (sorting rules) make character comparisons complicated. Integers are very good when using as an index column." - HottestGuide

StackExchange Database Administrators Q#15918, answer score: 2